Scheme Modernization for the Evacuation of Noncondensable Gases from Delivery Water Heaters of Cogeneration Turbines

The cogeneration turbine vacuum system contains both a condenser and delivery water heaters (DWHs). When the steam pressure in the lower heat extraction is below the barometric pressure, an additional amount of air enters DWH-1, which is then evacuated into the condenser. This can lead to an increase in vapor pressure within the condenser and an increase in the oxygen content of the main condensate, especially when air flowing at a significant rate is evacuated into the condenser. To increase the efficiency of the cogeneration plant, a special ejector (two-stage with a pre-cooler) was developed and installed at the Combined Heat Power Plant (CHPP) to evacuate noncondensable gases from the DWH. This ejector implements technical solutions that aim to improve the efficiency and reliability of the system. The ejector is connected through cooling water to the main condensate line behind the main ejectors. Heating steam drained from the ejector is removed into the DWH-1 condensate tank, and the estimated pressure at the evacuation of the ejector, P n , is 25 kPa. The transfer of air sucked from the DWH to the DWH ejector results in a 0.12 kPa decrease in the vapor pressure within the condenser. In addition, steam is saved for the turbine’s auxiliaries because the amount of steam consumed by the DWH ejector is five times lower than that of the main turbine ejector. With small amounts of sucked air, a single-stage version of the DWH ejector can be employed, as the pressure ratio between the outlet of ejector stage 1 and the pressure in the stage 1 receiving chamber 1 is lower than 1. However, to shut down stage 1 of the ejector, it would be necessary to install an individual valve on the stage 1 steam supply pipeline.